1. Field of the Invention
The present invention is related to an LED lighting device having multiple driving stages, and more particularly, to an LED lighting device having multiple driving stages for providing wide effective operational voltage range without causing flicker and uniformity issue.
2. Description of the Prior Art
An LED lighting device directly driven by a rectified alternative-current (AC) voltage usually adopts a plurality of LEDs coupled in series in order to provide required luminance. As the number of the LEDs increases, a higher forward-bias voltage is required for turning on the LED lighting device, thereby reducing the effective operational voltage range of the LED lighting device. As the number of the LEDs decreases, the large driving current when the rectified voltage is at its maximum level may impact the reliability of the LEDs.
An LED lighting device is configured to modulate luminous flux and intensity. This time variation is commonly referred to as flicker. LED flicker, whether perceptible or not, has been a concern of the lighting community because of its potential human impacts, which range from distraction, mild annoyance to neurological problems. Therefore, there is a need for an LED lighting device capable of improving the effective operational voltage range, the reliability and the flicker phenomenon.